Four specific aims are proposed: 1) to isolate and characterize the plasma membrane fraction of cultured Sertoli cells; 2) to produce monoclonal antibodies directed against Sertoli-cell specific antigens; 3) to isolate and biochemically characterize these antigens; and 4) to characterize Sertoli cell subpopulations which may or may not express a particular antigen. Monoclonal antibodies will be screened by an ELISA assay and selection methods are proposed for Sertoli cell specific antigens, a Sertoli cell developmental antigen and for the FSH receptor. The fluorescence activated cell sorter (FACS) will be used to isolate subpopulations of Sertoli cells on the basis of the ability of the cell to bind to a particular antibody. The presence of subpopulations of Sertoli cells may reflect a functional heterogeneity of the cells in vivo which may be related to the association of Sertoli cells with differnet parts of the spermatogenic cycle. The acquisition of the proposed antibodies and the characterization of the antigens should provide important information on the development and function of Sertoli cells during spermatogenesis.